1. Field of the Invention
The present invention relates to seismic pulse generation and, more particularly, to seismic pulse generators for use, for example, in both on-shore and off-shore exploration.
2. Description of the Related Art
One kind of seismic pulse generator with which the invention is concerned, although not exclusively, is that which basically includes a two-chamber device in which a "driver" gas at relatively high pressure in one chamber is employed to generate a shock wave in the other, adjoining, chamber which contains a different gas which is at relatively low pressure. The chambers are not allowed to communicate with each other until the generator is operated. Communication between the two chambers may be prevented for example by means of a releasable shuttle valve member which in the closed position closes an opening between the chambers. When the shuttle valve member is abruptly released from this closed position, to allow communication, a shock wave is generated and propagates in the low pressure chamber as a result of the impact of the high pressure gas onto the low pressure gas. This kind of generator is also referred to as a seismic shock gun. In prior art devices the release of the shuttle valve member from the closed position mentioned above may be initiated by releasing a pressure release member to allow the release of a small portion of the high pressure gas rearwardly from the generator. The pressure release member may be, for example, a poppet-valve or a flap valve as described in Applicant's earlier GB patent specifications nos. 2165945B and 2230860B, respectively.
An object of the invention is to provide a construction of seismic pulse generator which facilitates repeatable firing.